For me it is a great balance between offense and defense, which I look at as having no safe zones (Aim High was a good example of this) or a limited amount of them. Safe zones can be good things though, don’t get me wrong, but having lots of them like in Logomotion or Ultimate Ascent made it a little bit annoying to see less defense being played. This is more of a personal thing than a general opinion, I know lots of people don’t like defense.
Another thing is having all tiers of teams be able to contribute in some way. I’m competing in VEX this year and teams who were having trouble building a good lift system were completely useless, since the floor goals are so small (I don’t want to start a rant about the current VEX game but it’s a good example of a game where it is hard to play defense or play at all if you aren’t a really good team).
An easy game to explain to people or just understand after watching a match or two is great. Games like Aerial Assist and Ultimate Ascent (and most other recent years) have been very good about this, where you could explain the basic gameplay in a sentence or two.
I also personally like games where there are lots of different tasks you can do, such as FIRST frenzy (2004), Ultimate Ascent, and if you know what savage soccer is, their game from last year was great for this (if you don’t know I can post a link).
Those are my personal thoughts, and may not reflect the FIRST community as a whole.